Conventional ball valves are mounted in a rigid seat or seal, which is a primary seal and which may be backed by O-rings to act as a secondary seal. Alternatively, other, specially configured elastomeric rings of special geometry can be used to insure that the ball remains sealed during operation of the valve. In many valves, however, only the seal on the pressurized side of the valve is maintained in contact with the ball while the other seal tends to "float".
When employed in an aircraft lavatory system, the ball valve seals may both be under pressure at different times and accordingly, these seals must be kept in close contact with the ball valve surface at all times, which tends to increase the drag or frictional resistance to the actuation of the valve.
An additional problem encountered by the seals that are utilized in aircraft lavatory systems is the hostile environment created by the chemicals that are found in the flushing solutions and other fluids that are found in such a system. These chemicals frequently react with the conventional elastomers heretofore in use in the valve seats and seals and cause swelling and possibly disintegration of such seats and seals.
The swelling of the seats or seals increases any existing drag or friction and therefore increase the requisite actuation forces. This may result in exceeding the allowable operating limits of the actuation or linkage mechanisms which have been designed to open and close the valve.